1. Related Conventional Arts
FIGS. 10A and 10B show engine fuel supply systems 100 according to related conventional arts, respectively.
FIG. 10A shows a cylinder fuel supply device 110 for supplying fuel into a cylinder of an engine 2 via a feed pump 1. FIG. 10B shows an HC (hydrocarbon) dosing device 120 for supplying fuel to an exhaust pipe 4 of an engine 2.
In the cylinder fuel supply device 110 shown in FIG. 10A, fuel in a fuel tank 5 is sucked by the feed pump 1 via a supply passage 10a, a pre-filter 6, and a supply passage 10b. The feed pump 1 discharges the fuel to a supply passage 10c after raising the pressure of the fuel to a predetermined fuel pressure, for example to about 3 to 5 kgf/cm2. The fuel the pressure of which has been raised by the feed pump 1 is sucked into a supply pump 8 via the supply passage 10c, a main filter 7, and a supply passage 10d. The supply pump 8 discharges the fuel to a supply passage 10e after further raising the pressure of the fuel to a predetermined fuel pressure, for example to about 1000 to 1600 kgf/cm2. The fuel the pressure of which has been raised by the supply pump 8 is supplied into a cylinder of the engine 2 via the supply passage 10e by a common rail and an injector (not shown). The engine 2 is operated by the high-pressure fuel being injected into the cylinder of the engine 2. If the fuel overflows in the supply pump 8, the excess fuel is discharged to the fuel tank 5 via an overflow fuel discharge passage 11.
When so-called “running out of gas” occurs, in other words, when the fuel in the fuel tank 5 has run short during operation of the engine 2 and the fuel supply to the engine 2 is stopped, or when the pre-filter 6 or the main filter 7 is replaced, air may be entrapped in a cylinder fuel supply passage 10. If air is entrapped in the cylinder fuel supply passage 10, the pressure of fuel flowing through the cylinder fuel supply passage 10 will not be raised to an adequate level for a long period of time until the air is completely removed from the cylinder fuel supply passage 10, leading to malfunction of the engine 2 or even difficulty in starting the engine. Therefore, a priming pump 9 need be activated periodically, every time after the fuel filter is replaced, for example every time the engine 2 has operated for 500 hours, or when running out of gas occurs, in order to remove the air before the engine 2 is operated.
Upon a switch 12 being turned on, a relay 13 is energized and the priming pump 9 is activated. Since air removal must be performed in the state where the engine 2 is not in operation, the priming pump 9 is activated while the engine 2 is not in operation.
Upon the priming pump 9 being activated, fuel in the fuel tank 5 is sucked into a suction port 9b of the priming pump 9 via the supply passage 10a, the pre-filter 6, the supply passage 10b, and a fuel suction passage 30. The priming pump 9 raises the pressure of the fuel to a predetermined fuel pressure suitable for air removal, for example to about 3 to 5 kgf/cm2, and discharges the fuel into an air-removal fuel supply passage 31 through a discharge port 9a. The fuel the pressure of which has been raised by the priming pump 9 is fed under pressure to the main filter 7 via the air-removal fuel supply passage 31, passes through the supply pump 8, and is discharged into the fuel tank 5 via the overflow fuel discharge passage 11. On the other hand, the fuel the pressure of which has been raised by the priming pump 9 is fed under pressure to the main filter 7 via the air-removal fuel supply passage 31, and is discharged into the fuel tank 5 via an air-removal fuel discharge passage 32. This removes air from the inside of the cylinder fuel supply passage 10.
Next, the HC dosing device 120 shown in FIG. 10B will be described.
Due to recent tighter regulations on exhaust gas of the engine 2, a diesel particulate filter 14 serving as an exhaust gas aftertreatment device is provided within the exhaust pipe 4. The diesel particulate filter 14 collects particulate matter (PM) contained in exhaust gas from the engine 2, whereby atmospheric diffusion of the particulate matter is restrained.
However, as the diesel particulate filter 14 is used for a long time to collect the particulate matter PM, the pressure loss in the exhaust pipe 4 will be increased, leading to difficulty in discharge of exhaust gas, and the filter will be clogged, resulting in deterioration of the function of the diesel particulate filter 14. Accordingly, the particulate matter PM deposited in the diesel particulate filter 14 must be removed to recover the function of the diesel particulate filter 14 at regular intervals, for example every time the engine 2 has operated for several tens of hours. Such recovery of the diesel particulate filter 14 can be performed by various methods, including “HC dosing” method.
It is well known that in order to remove the particulate matter PM deposited in the diesel particulate filter 14, the temperature of the exhaust gas is increased to burn soot in the particulate matter PM clogging the filter. For this purpose, an oxidation catalyst 15 is disposed before the diesel particulate filter 14 in the exhaust pipe 4, and the fuel is sprayed to the oxidation catalyst 15 so that oxidation reaction occurs between HC (hydrocarbon) in the fuel and the oxidation catalyst 15 to generate heat and thus to raise the temperature of the exhaust gas.
The HC dosing device 120 is provided for supplying fuel into the exhaust pipe 4 for the purpose of recovering the function of the diesel particulate filter 14.
A controller 50 is provided to determine it is time to recover the function of the exhaust gas aftertreatment device (hereafter, referred to simply as the “recovery time”) on the basis of a detection signal from a sensor 51, and upon determining so, applies a signal to command fuel supply into the exhaust pipe 4 to the HC dosing pump 16 and valves 17 and 19. As the HC dosing pump 16 is thus activated, the valves 17 and 19 are opened. Since the fuel supply into the exhaust pipe 4 must be performed in the state where the engine 2 is in operation and the exhaust gas is discharged, the HC dosing pump 16 is activated while the engine 2 is in operation.
Upon the HC dosing pump 16 being activated, the fuel in the fuel tank 5 is sucked into a suction port 16b of the HC dosing pump 16 via a fuel suction passage 41.
The HC dosing pump 16 raises the pressure of the fuel to a predetermined fuel pressure suitable for supply into the exhaust pipe, for example to about 7 to 10 kgf/cm2, and then discharges the fuel to a passage 20a through a discharge port 16a. The fuel the pressure of which has been raised by the HC dosing pump 16 is injected and supplied into the exhaust pipe 4 via the supply passage 20a, the second on-off valve 17, a flow control valve 19, a supply passage 20b, and a nozzle 21.
2. Prior Related Arts Described in Patent Documents
Patent Document 1 listed below discloses an invention wherein a pump exclusively for air removal is provided in addition to a feed pump so that air removal from a fuel system of a diesel engine is performed by operating this pump.
Inventions relating to the above-described HC dosing device are disclosed in Patent Documents 2 and 3 listed below.
Further, a technique for supplying fuel to an exhaust pipe in the same manner as the above-described HC dosing device is found in Patent Document 4 listed below. This Patent Document 4 discloses an invention wherein an exhaust pipe is provided with a catalyst for removing NOx contained in exhaust gas, and light oil fuel serving as a reducing agent with respect to the catalyst is injected under high pressure into the exhaust pipe in order to enhance the NOx removal efficiency of the catalyst.    Patent Document 1: JP H2-256869A    Patent Document 2: JP H5-34486A    Patent Document 3: JP 2000-193824A    Patent Document 4: JP H8-68315A